Human accessory cells have a humoral bystander effect on CAFC growing on murine feeder.

Human early hematopoietic progenitors from bone marrow (BM) and leukapheresis products (LP) are highly proliferative in presence of accessory cells in standard culture on the murine FBMD-1 cell feeder with weekly addition of human interleukin-3 (HuIL-3) and granulocyte-colony stimulating factor (HuG-CSF). If however purified CD34+ cells are cultured under otherwise identical conditions, cobblestone areas (CAFC) formed by the same number of target cells are diminished by more than 1 log, as we showed previously. This suggests that mature cells are involved in growth of early progenitors. To determine whether this bystander effect is mediated by soluble growth factors, or by direct cell-to-cell contact with early progenitors, we stimulated mature plastic adherent cells separately and tested the resulting conditioned supernatant (ACS) on CAFC and colony-forming unit-granulocyte-macrophage (CFU-GM) production. In ACS-complemented standard cultures of purified CD34+ cells, the yield of CAFC was up to 1 log higher if compared to parallel cultures without ACS. Likewise, the CFU-GM production was enhanced in presence of ACS, especially in the adherent fraction of the culture. When CD34+ cell cultures were performed with ACS but without added interleukin-3 (IL-3) and granulocyte colony-stimulating factor (G-CSF), CAFC production was in the same range as if these growth factors were added alone. Addition of anti-G-CSF antibody (Ab) to ACS decreased CAFC recruitment significantly, whereas anti-IL-3 Ab had no significant effect. These findings suggest that ACS complemented with IL-3 and G-CSF replaces the accessory cells largely; this is not only due to presence of G-CSF, because ACS in combination with recombinant growth factors mounts CAFC yield higher than saturating amounts of growth factors alone do. There must be further synergizing soluble factors in the supernatant.

Mature accessory cells influence long-term growth of human hematopoietic progenitors on a murine stromal cell feeder layer.

A recently described long-term culture system for early human progenitor cells was established with the murine preadipocyte stromal line FBMD-1 grown in 96-well plates; cobblestone areas formed by inoculated hematopoietic cells are determined in a limiting dilution setting after five weeks' culture. To compare the capacity of cobblestone-area-forming cell (CAFC) formation by bone marrow and leukapheresis products in this system, mononuclear cells (MNC) of both origins were cultured. As related to CD34+ cell content, CAFC yields after five weeks' culture were in the same range in bone marrow and leukapheresis stemming from patients with efficient mobilization of hematopoietic cells. In purified CD34+ cell fractions, the CAFC yield per inoculated cell number was considerably higher than in MNC; however, if the CAFC number was related to the inoculated CD34+ cell number in MNC and after purification, the yield was four to eight times decreased in purified fractions. Addition of the mature cells brought the CAFC yield back up to the numbers obtained in the unseparated MNC fraction. By contrast, slightly more advanced progenitors per CAFC were found in cultures of purified hematopoietic cells from both origins than in whole MNC. The results suggest that mature human accessory cells give noticeable support to recruitment of early progenitors on this feeder but lead to lower yield of GM progenitors.

Adhesion and Transendothelial Migration of Human Monocytes: Role of Cytokine (IL3, GM-CSF) Activated Endothelial Cells.

In this study we have investigated the effect of GM-CSF and IL3 on Human Umbilical Vein Endothelial Cells (HUVEC). We studied the adhesion properties of HUVEC for non stimulated human elutriated monocytes, as well as the transendothelial migration of these cells. We analysed the expression of adhesion molecules (VLA4/CDw49d, VCAM1/CD106, LFA1/CD11a, ICAM1/CD54, CD18, L-selectin/CD62L, PeCAMl/CD31, ELAM1/CD62E) induced in monocyte adhesion and transmigration. Optimal conditions of HUVEC stimulation with IL3 and GM-CSF were obtained with 100 U/ml of each cytokine. IL3 and GM-CSF were found to induce HUVEC proliferation, more than twofold at day 7 of the culture compared to controls. HUVEC proliferation was not stimulated by IL1α, a slight inhibitory effect was observed at 250 and 500 U/ml. We showed that GM-CSF, IL3 and their combination mimic on activation like status that on which is expressed by an enhancement of adhesion and migration of non stimulated monocytes to and across cytokines activated HUVEC monolayers. After 6 hours activation with IL3 or GM-CSF, more than 60% of the monocytes are adherent to HUVEC after a contact of 30 minutes (vs 30.8 ± 4.6% for untreated control HUVEC). This percentage increased to 80% after a 7 days culture period in presence of the same cytokines (vs 40 ± 5.1% for untreated control HUVEC). IL3 was very effective at inducing monocyte transendothelial migration. The potency of IL3 is seen to be 2 to 3 fold higher than GM-CSF in this system. GM-CSF and IL3 modulate on HUVEC the expression of adhesion molecules induced in monocyte adhesion and transendothelial migration processes. We showed that anti-ELAMl inhibit in part monocyte migration (8.5 ± 3% vs 46.33 ± 4.03% without MoAb; vs 5.1 ± 2% with ICAM1, ELAM1 and VCAMI MoAbs).